There are a few routes I recommend.

Good Omens is nice if you already like Neil Gaiman and want to branch in a Pratchett-ward direction.

The Watch series of Discworld is great if you like urban fantasy with a little mystery and a focus on cops in a Fantasy world. Plus Vimes is one of the best characters in Fantasy.

Small Gods is a great standalone poking fun at religion in a lot of pretty insightful ways. Great for trying out Pratchett's style without feeling the need to devote to a series.